Inhibition of corrosion



Patented Apr. 15, 1941 INHIBITION OF CORROSION Frank G. Keenen, Wilmington, Del., assignor to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware No Drawing.

ApplicaticnMay 21, 1937,

Serial No. 143,935

3 Claims.

This invention relates to the inhibition of corrosion by solutions of ammonium compounds and, more particularly, to the inhibition of corrosion of ferrous materials subject to attack by solutions of ammonium nitrate.

It is known that ammoniacal solutions of ammonium compounds such as ammonium nitrate exert a deleterious corrosive effect upon ferrous materials of construction.

Previously recourse has been had to the use of the noble metals, expensive alloys or lined equipment in order to overcome this corrosive effect. This procedure has, in turn, resulted in placing an uneconomical cost disadvantage upon the handling of such solutions.

It is an object of the present invention to overcome the problems above outlined and to provide an improved method for inhibiting corrosion by solutions of ammonium compounds.

It is a further object of this invention to provide an improved method of inhibiting corrosion of ferrous materials subject to corrosion by solutions of ammonium nitrate.

Other objects and advantages of the invention will be apparent by reference to the following specification wherein its details and preferred embodiments are described.

According to the present invention corrosion of ferrous materials which are subject to attack by solutions of ammonium nitrate can be greatly reduced by addition to such solutions of a compound containing sulfur as one of its constituent elements. I have found, for example. that relatively small concentrations of a great multitude of both organic and inorganic compounds which contain sulfur will effectively inhibit corrosion of ferrous materials in contact with solutions of ammonium nitrate. Although as indicated, the number of sulfur-containing compounds tested has been large, I have found that generally speaking sulfur-containing compounds in which the sulfur is either dior tetravalent are the most effective. This rule or generality has exceptions in that some compounds containing sulfur of different valency, such as hexavalent sulfur, are equal in effectiveness to those of dior tetravalent sulfur, but generally the latter named valencies appear preferable.

According'to this invention all aqueous solutions of ammonium nitrate whether ammoniacal or not, or solutions of ammonium nitrate in other liquids, such, for example, as in anhydrous formamide. hydrocyanic acid, ammonia. or combinations thereof, may be inhibited in their corrosive effect upon ferrous materials by use of sulfur or sulfur-containing compounds. The inhibitory action of the materials of this invention. I have found, is effective in such solutions of ammonium nitrate whether or not other salts are also present such as other nitrates, urea, acetamide or the like.

In utilizing the terms ferrous materials, I mean to include within the scope of this invention high carbon and low carbon steels generally, boiler plate, cast iron, malleable cast iron, wrought iron, puddled wrought iron, austenitic steel, and copper-, molybdenumand nickelcontaining steels or combinations thereof. In fact, all ferrous materials which are corrodible by ammoniacal ammonium nitrate solutions are included within the scope of this invention. The corrosion of chromiumand vanadium-containing steels is, I have found. very slight and at least no greater than the previously mentioned materials. the corrosion of which has been inhibited by the corrosion inhibitor of this invention. Therefore, although the present invention is applicablein the case of such alloys, the present invention probably will not be applied in such cases because the corrosion does not warrant its application.

The concentration of the inhibitor used may vary over a wide range although I have found that relatively small quantities are effective. Thus. for example. the use of as small an amount as from 0.01 to 0.2% of inhibitor, based upon the weight of the corrosive liquid. will reduce the corrosion of ferrous materials subject to contact with aqueous ammoniacal ammonium nitrate solutions by as much as 95-98%.

. As previously indicated, I have discovered that inorganic as well as organic compounds of sulfur are effective inhibitors. Thus, for example, I have found among the inorganic compounds that relatively small concentrations of the following are effective corrosion inhibitors, as hereinbefore described, when present in ammonium nitrate solutions:

Oxides of sulfur, such as sulfur dioxide.

Sulfldes, such as: mono-, di-, triand polysulfides; more specifically alkali metal sulfides, such as sodium, potassium, lithium and ammonium sulfide; hydrogen sulfide; alkaline earth sulfides, such as calcium and barium sulfide and the like.

Sulfur chlorides, such as thionyl chloride (SOC12) and sulfur chloride (SzClz).

Sulfamide, (NH2)SO2.

Sulfurous acid and its salts, such as sulfites and bisulfites, for example sodium sulfide, sodium bisulfite, calcium sulfite and the like.

Hypo sulfites, i. e. derivatives of hyposulfurous acid (HzSzOi) such as sodium hyposulfite (Na-25204).

Thiosulfatcs, i. e. derivatives of thiosulfuric acid (HzSzOa) such as the ordinary hypo," NazSzOa.

Derivatives of pclythionic acids, such as the di, tri-, tetraand pentathionates, vNazaSzOa, NazSsOs, Na2S4Os and Na2S5Oe.

Pei-sulfuric acid and persulfates.

sulfates and bisulfates.

These listed inorganic substances, and derivatives thereof, I have found to be very effective, but I have also found that organic compounds containing sulfur are equally if not more effective in many instances. The organic compounds hereinafter set forth are but representative and, altho in the majority they are of the aliphatic class of compounds, this must not be taken as a limitation to the aliphatic class, for aromatic sulfur compounds are likewise desirable and effective inhibitors according to this invention.

Among the organic sulfur compounds I have found effective according to this invention are:

Mercaptans, such as butyl and lauryl mercaptan, ethyl dimercaptan, thiocresol, and the like.

Mercaptals or thioaldehydes, such as thiobenzaldehyde.

sulfides and disulfides, such as dicyclohexyl sulfide, tetramethylthiuram disulflde, carbon disulfide, dibenzyl disulfide and the like.

Sulfoxides, such as ethyl disulfoxide.

Sulfonium compounds, such as mercaptobenzothiazole methyl sulfonium methyl sulfate and the like.

Sulfur derivatives of hydroazy organic acids, such as thioglycolic acid.

Sulfonic acids and their derivatives, such as lauryl phenyl sodium sulfonate.

Thiosulfonates, such as ethyl thiosulfonate.

Thiocyanates, such as methyl thiocyanate.

Isothiocyanates (mustard oils).

Thiazoles, such as mercaptobenzothiazole and its derivatives.

Sulfur derivatives of carbonic acids, such as: the mono-, di-, xanthates such as potassium xanthate; butyl ethyl minerec (xantho ether); thiocarbamates and dithiocarbamates such as sodium octyl dithiocarbamates, dicyclohexyl ammonium dicyclohexyl dithiocarbamate; thiuram derivatives, such as tetra methyl thiuram disulfiide; thioureaand derivatives such as phenyl-thiourea, diortho tolyl thiourea; thioamides, and the like.

Sulfur derivatives of carboxylic acids.

and trithiocarbonates; the

Sulfur dye colors, such as sulfogene compounds,

and the like.

The concentration of inhibitors, such as above outlined, may be varied over a wide range, as much being utilized as desired, but I prefer to ultilize a relatively small quantity, say, an amount corresponding to about 0.01 to 0.2% of the ammonium nitrate solution the corrosive effect of which is being inhibited.

The effectiveness of the inhibitors of this invention may be illustrated by the fact that although mild steel, when in contact with a solutionof ammonium nitrate containing about 60 parts by weight ammonium nitrate, 20 parts water and 20 parts ammonia, is corroded to the extent of -150 milligrams loss of material per square centimeter per month, a concentration of from 0.01 to 0.2% of an inhibitor of this invention, such as thiourea will reduce corrosion by the same ammonium nitrate solution to 3-5 milligrams per square centimeter per month. By adding the inhibitors of this invention to ammonium nitrate solutions, either before or after filling a tank car or other container, preferably by mixing such inhibitors with the liquid immediately upon production, it is thereby possible to make economically feasible the safe handling thereof in commerce without recourse to highly expensive materials of construction.

The destructively corrosive effect of ammonium nitrate solutions upon containers therefor such as tank cars, drums, and the like will be appreciated and, likewise, the value of the present invention in so greatly reducing corrosion will be apparent.

Various changes may be made in the details and proportions of materials of this invention without departing therefrom or sacrificing any of the advantages thereof.

I claim:

1. The method of inhibiting the corrosive effect of ammoniacal ammonium nitrate solutions upon ferrous materials, said solutions containing sufficient ammonium nitrate to be normally corrosive to ferrous materials, which comprises adding to such solutions a small quantity of thiourea, the thiourea being added in sufiicient amount to substantially prevent corrosion.

2. A container, having internal surfaces of ferrous material, having therein an ammoniacal ammonium nitrate solution containing sufiicient ammonium nitrate to be normally corrosive to ferrous materials, said solution containing thiourea in sufiicient amount to substantially prevent corrosion.

3. The process of reducing corrosion of ferrous metals by a solution of ammonium nitrate containing free ammonia which corrodes said ferrous metals, which comprises dissolving thiourea in said solution in amount sufficient to materially decrease the rate of corrosion of a ferrous metal by said solution, and contacting said solution with said ferrous metal.

FRANK G. KEENEN. 

